.\" $Id: curl_multi_perform.3,v 1.8 2006-09-21 11:09:54 bagder Exp $
.\"
.TH curl_multi_perform 3 "1 March 2002" "libcurl 7.9.5" "libcurl Manual"
.SH NAME
curl_multi_perform - reads/writes available data from each easy handle
.SH SYNOPSIS
#include <curl/curl.h>

CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);
.ad
.SH DESCRIPTION
When the app thinks there's data available for the multi_handle, it should
call this function to read/write whatever there is to read or write right
now. curl_multi_perform() returns as soon as the reads/writes are done. This
function does not require that there actually is any data available for
reading or that data can be written, it can be called just in case. It will
write the number of handles that still transfer data in the second argument's
integer-pointer.

When you call curl_multi_perform() and the amount of \fIrunning_handles\fP is
changed from the previous call (or is less than the amount of easy handles
you've added to the multi handle), you know that there is one or more
transfers less "running". You can then call \fIcurl_multi_info_read(3)\fP to
get information about each individual completed transfer, and that returned
info includes CURLcode and more.
.SH "RETURN VALUE"
CURLMcode type, general libcurl multi interface error code.

If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this basically means that you
should call \fIcurl_multi_perform\fP again, before you select() on more
actions. You don't have to do it immediately, but the return code means that
libcurl may have more data available to return or that there may be more data
to send off before it is "satisfied". Do note that \fIcurl_multi_perform(3)\fP
will return \fICURLM_CALL_MULTI_PERFORM\fP only when it wants to be called
again \fBimmediately\fP. When things are fine and there are nothing immediate
it wants done, it'll return \fICURLM_OK\fP and you need to wait for \&"action"
and then call this function again.

NOTE that this only returns errors etc regarding the whole multi stack. There
might still have occurred problems on individual transfers even when this
function returns \fICURLM_OK\fP.
.SH "TYPICAL USAGE"
Most applications will use \fIcurl_multi_fdset(3)\fP to get the multi_handle's
file descriptors, then it'll wait for action on them using \fBselect(3)\fP and
as soon as one or more of them are ready, \fIcurl_multi_perform(3)\fP gets
called.
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
.BR curl_multi_fdset "(3), " curl_multi_info_read "(3), "
.BR libcurl-errors "(3)"
